Toner loading for touchdown donor

ABSTRACT

In an electrostatic development system, developer material in a sump comprises a mix of toner particles adhered to magnetic carrier particles. A transfer member, disposed in the trough of the sump, removes developer material in the form of a magnetic brush. A doner member, operatively associated with the transfer member and a photoreceptor having the electrostatic latent image to be developed, is biased whereby to strip toner particles from the carrier particles on said transfer member and to deliver said stripped toner particles to the latent image.

United States Patent [191 Liebman TONER LOADING FOR TOUCHDOWN DONOR [75] Inventor: Alan J. Liebman, Rochester, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

22 Filed: Nov. 28, 1973 21 Appl. No.: 419,732

[52] US. Cl 118/637; 101/DIG. 13; 346/74 ES; 355/3 DD [51] Int. Cl. G03G 13/06 [58] Field of Search 96/1 SD; 117/175; 1l8/637; l0l/DIG. 13; 346/74 ES; 355/3 DD [56] References Cited UNITED STATES PATENTS 10/1968 King et al. 118/637 5/1971 Yang 355/15 Dec. 30, 1975 3,654,902 4/1972 Hakanson 118/637 3,696,783 10/1972 Fantuzzo ll8/637 3,759,222 9/1973 Maksymiak et al 1. 118/637 Primary ExaminerMorris Kaplan 571 ABSTRACT 6 Claims, 1 Drawing Figure US. Patent Dec. 30, 1975 3,929,098

TONER LOADING FOR TOUCHDOWN DONOR DESCRIPTIONOF THE INVENTION 1 This invention is concerned with an improvement to a touchdown development system. The term touchdown development as used in thisapplication refers to the following system: i l

A toner laden rotating donor member (which may be a roller or an endless belt) is located adjacent to a moving photoreceptive surface bearing a latent electrostatic image thereon. The donor member is spaced from the photoreceptor so that a gap of about to 8 'mils exists between the toner layer surface and the photoreceptive surface. The toner on the donor member is given a charge in polarity opposite to the polarity of the electrostatic latent image; As the donor member carries toner past the latent image, the toner is attracted from the donor to the image to develop the image.

One of the main problems in prior touchdown development systems is loading the donor roll with an adequate amount of toner to provide a developed image of an acceptable density.

It is an object of this invention to provide means to load a donor roll with an adequate amount of' toner which will result in the development of 'an electrostatic latent image with an acceptable density.

It is a further object of .this invention to provide means for loading a donor member with. an adequate amount of toner which will result in the development of an electrostatic latent image of acceptable density. A more detailed relatedobject is to provide a method and meansfor loading the donor member with a generally uniform layer of toner particles which will result in a generally uniform development of the electrostatic latent image. P

It is stilla further object of the invention to provide a touchdown development system where unused toner particles returned to a developer sump after being presented to a latent image are not agglomerated.

Other objects of this invention will become apparent from the following description with reference to the drawing wherein:

The sole figure is a schematic view of a touchdown development system.

Referring to the drawing, there is shown a xerographic reproduction system utilizing the concept of the present invention. In this apparatus, a xerographic photoreceptor plate is in the form of a drum 10 which passes through stations A-E in the direction shown by the arrow. The drum has a suitable photosensitive surface on which a latent electrostatic image can be formed. A plurality of stations about the periphery of the drum which carry out the reproduction process are: charging station A, exposing station B, developing station C, transfer station D, and cleaning station E. These stations represent conventional means for carrying out their respective functions and do not form a part of the present invention.

At station A, a corona charging device 12 places a uniform electrostatic charge on the photosensitive material. As the drum 10 rotates, a light pattern, by a suitable exposing apparatus 14, is exposed onto the charged surface of the drum 10. The latent image thereby formed on the surface of the drum is developed by the application of toner particles 15 by a donor member 16 at the developing station C. After the image is developed at station C, it passes through transfer stationD, wherein the toner is transferred to a sheet 17.

A corona charging device 18 is utilized in the normal way to facilitate transfer and fuser device 20 is provided to fuse the toner to sheet 17. Following transfer of the developed image to the copy sheet, the drum rotates through cleaning station E, comprising cleaning brush,22 which cleans residual toner particles from the drum 10.

A developer sump 26 containing a developer mix 28 therein is located below the donor member 16. The developer mix comprises toner particles 15 and ferromagnetic carrier particles. The toner particles and the carrier particles are selected that the toner particles will become triboelectrically charged to'a polarity op posite the charge of the latentimage upon mixing with the carrier particles. In this particular instance, if the charge of the latent image is positive then the triboelectric charge on the tonerparticles will be selected to be negative. Any type of agitating means may be provided for agitating the developer mix in the sump -to create the proper triboelectric charge on the toner particles. A magnetic brush in the form of a cylinder housing.30 is provided between the donor 16 .and the developer. sump 26 and arrangedthat a portion thereof will rotate through the developer mix. A pickup magnet- 3l ,and a developing magnet 32 are provided on a stationary iron keeper 33 within the cylinder housing 30. The magnets, 31 and 32 are arranged so that, upon rotation of the cylinder housing 30 through the developerbed, magnetic carrier particles with toner triboelectrically attached thereto will be picked up by the cylinder housing at those portions corresponding to the magnetic field of pickup magnet 31-and brought adjacent to the outer surface of the donor member 16 and within the magnetic field of development magnet 32. which causes thedeveloper bristles on the brush 30 to become erect. Upon further rotation of the magnetic brush 30, the unused toner particles as well as the magnetic carrier particles carried thereby are brought outof thefleld of the magnet 32 whereby they fall bygravity back into the developer sump where the carrier particles can be retoned with toner particles. g

If only toner particles were present inthedeveloper system, agglomeration of the toner particles would tend to occur in a toner bed during rotation of the cylinder 30 therethrough and upon presentation of the toner particles by cylinder 30 to the donor 16 and by the cylinder 30 to a latent image with the unused toner falling back into the sump being agglomerated. However, the presence of carrier particles in the development system helps to prevent this tendency to agglomerate.

In order to create an electrical field for developing or loading the donor 16 with toner particles, and assuming that the latent image carries a positive charge, the magnetic brush 30 is biased to 6OO volts and the donor 16 is biased to +200 volts which is approximately the background potential on the drum 10. This field effects transfer of the negative toner particleslS to the donor 16 from the carrier particles as the developer is pres ented to the donor by the magnetic brush 30.

Since there is a possibility that the carrier particles may be mechanically impressed onto the donor, a carrier trap 36, which is in the form of a magnetic roller, is rotatably located adjacent the drum to pick off any carrier particles 38 which may be on the donor 16. A scraper member 40 engages the roller 36 to scrape any carrier particles on the roller 36 therefrom. The carrier particles 38 scraped from the pick-off roller 36 fall by gravity back into the sump 26 for retoning. A scraper member 42 is provided to scrape residual toner particles from the donor 16 which fall back into the sump 26.

The carrier particle size distribution should be such that at least 85%, preferably 95%, of all of the particles, by volume, are less than 50 microns average diameter and preferably between and 50 microns. This is necessary in order to coat the donor [6 with a generally uniform layer of toner particles. It has been found that when larger size carrier particles are utilized, numerous carrier bead tracks which were relatively wide and deep were formed in the toner layer on the donor drum 16. When carrier particles of the size specified above are utilized, thinner and shallower carrier tracks were formed in the deposited toner layer which were insignificant insofar as disturbing the uniformity of the toner layer on the donor drum 16. It is very advantageous to essentially eliminate the carrier bead tracks in the toner layer'since those areas of the latent image which correspond to the tracks as the toner layer is presented thereto will not be developed or at the most will be just slightly developed resulting in a poor copy in those developed areas. For instance, a typical line type written'char'acter is about 250 microns wide. It has been foundthat with a carrier bead track in a toner layer which is greater than about 20% of the character line width,there is a good chance that some of or all of the character will be lost in development. Thus, the use of carrier particles or beads of the size specified above assures that the character will not be partially or fully lost during-development of the latent image.

What is claimed is:

l. A development system for developing latent electrostaticimages carried by a photoreceptor of an electrostatic processor; said development system comprising the combination of a sump for storing a supply of developer, said developer including ferromagnetic carrier particles having toner particles triboelectrically attracted thereto; a rotatable doner member positioned adjacent said photoreceptor for applying toner particles. to said photoreceptor in conformity with said latent images; magnetic means disposed between said sump and said doner member for loading said doner member with toner particles; and means coupled to said doner member and said magnetic means for creating an electrostatic field between said magnetic means and said doner member for stripping the toner particles from the carrier particles during the loading of said doner member.

2. The development system of claim 1 wherein a rotatable magnetic means is located adjacent the surface of said doner member to magnetically attract any carrier particles carried by said donor member prior to said carrier particles being presented to said latent image, and means for removing said magnetic particles from said rotatable magnetic means.

3. The development system of claim 1 wherein the size distribution of said carrier particles is such that at least by volume, of all of the carrier particles in said sump are of a diameter less than 50 microns.

4. The development system of claim 3 wherein at least 85% by volume of all of said carrier particles in said sump are of a diameter between 10 and 50 microns.

5. A development system for developing latent electrostatic images carried by a photoreceptor of an electrostatic processor; said development system comprising the combination of a supply of developer including ferromagnetic carrier particles having toner particles triboelectrically attracted thereto, at least 85% by volume of all of said carrier particles having a diameter less than 50 microns; a doner member positioned adjacent said photoreceptor for developing said images with toner particles; and means disposed between said sump and said doner member for removing developer from said sump, stripping toner particles from the carrier particles of said removed developer and loading said toner member with a substantially uniform layer of said stripped toner particles.

6. The development system of claim 5 wherein at least 85% by volume of all of said carrier particles in said sump are of a diameter between 10 and 50 microns. 

1. A DEVELOPMENT SYSTEM FOR DEVELOPING LATENT ELECTROSTATIC IMAGES CARRIED BY A PHOTORECEPTOR FOR AN ELECTROSTATIC PROCESSOR; SAID DEVELOPMENT SYSTEM COMPRISING THE COMBINATION OF A SUMP FOR STORING A SUPPLY OF DEVELOPER, SAID DEVELOPER INCLUDING FERROMAGNETIC CARRIER PARTICLES HAVING TONER PARTICLES TRIBOELECTRICALLY ATTRACTED THERETO; A ROTATABLE DONER MEMBER POSITIONED ADJACENT SAID PHOTORECEPTOR FOR APPLYING TONER PARTICLES TO SAID PHOTORECEPTOR IN CONFORMITY WITH SAID LATENT IMAGES; A MAGNETIC MEANS DISPOSED BETWEEN SAID SUMP AND SAID DONER MEMBER FOR LOADING SAID DONER MEMBER WITH TONER PARTICLES; AND MEANS COUPLED TO SAID DONER MEMBER AND SAID MAGNETIC MEANS FOR CREATING AN ELECTROSTATIC FIELD BETWEEN SAID MAGNETIC MEANSS AND SAID DONER MEMBER FOR STRIPPING THE TONER PARTICLES FROM THE CARRIER PARTICLES DURING THE LOADING OF SAID DONER MEMBER.
 2. The development system of claim 1 wherein a rotatable magnetic means is located adjacent the surface of said doner member to magnetically attract any carrier particles carried by said donor member prior to said carrier particles being presented to said latent image, and means for removing said magnetic particles from said rotatable magnetic means.
 3. The development system of claim 1 wherein the size distribution of said carrier particles is such that at least 85%, by volume, of all of the carrier particles in said sump are of a diameter less than 50 microns.
 4. The development system of claim 3 wherein at least 85% by volume of all of said carrier particles in said sump are of a diameter between 10 and 50 microns.
 5. A development system for developing latent electrostatic images carried by a photoreceptor of an electrostatic processor; said development system comprising the combination of a supply of developer including ferromagnetic carrier particles having toner particles triboelectrically attracted thereto, at least 85% by volume of all of said carrier particles having a diameter less than 50 microns; a doner member positioned adjacent said photoreceptor for developing said images with toner particles; and means disposed between said sump and said doner member for removing developer from said sump, stripping toner particles from the carrier particles of said removed developer and loading said toner member with a substantially uniform layer of said stripped toner particles.
 6. The development system of claim 5 wherein at least 85% by volume of all of said carrier particles in said sump are of a diameter between 10 and 50 microns. 